VI. VELOCITY. 



VI. MEASUREMENT OF VELOCITY. 



A. LOGS AND CURRENT METERS. 



393. Patent Log. Massey. For measuring speed at sea ; 

 in use in H.M. Navy. 



Hydrographic Department of the Admiralty. 



394. Patent Log. Walker. For measuring speed at sea. 



Hydrographic Department of the Admiralty. 



396. Current Meter, for measuring the velocity of currents 

 in rivers at different depths. Elliott Brothers. 



An endless screw on a spindle turns two wheels at the same time, the one 

 recording every revolution of the blades by moving one division ; the other 

 indicating every complete revolution of the former. 



397. Rery's Current Meter, constructed for measuring the 

 velocity of currents in larger rivers. Elliott Brothers. 



The spherical boss is so determined that it will displace just as much water, 

 as to weight, as will balance the weight of all the parts which are fixed to the 

 spindle, so as to reduce friction to a minimum. Although the apparatus is 

 covered with glass, it has to be filled, before using it, with pure water to esta- 

 blish similarity of pressure inside and outside. After every experiment the 

 water is removed and the spindle thoroughly dried. This form of current 

 meter was used by Mr. Eery on the survey of the Parana and Uruguay rivers. 



397a. Darcy Pilot Gauge or Current Meter, for deter- 

 mining the velocity of streams of water. Prof. W. C. Unwin. 



The velocity is obtained by a single measurement, and no time observation 

 is required. Used in Darcy and Bazin's researches on the flow of water in 

 pipes and canals. 



398. Ramsten's Patent Ship's Log. Elliott Brothers. 



399. Water Meter, based on the principle of measuring the 

 volume of water by recording its speed. J. A. Midler , C.E. 



This water meter consists principally of an air and water-tight chamber or 

 vessel, wherein moves a float, carrying two magnets of equal power, and fixed 

 with their dissimilar poles in juxta-position to each other : the whole combina- 

 tion of the float and its spindle, together with the magnets, is made as near as 

 possible equal to the density or specific gravity of water. The water in passing 

 through this measuring vessel is forced to take a rotary motion, by means of 

 a screen or a tongue, being a metal piece, put at a certain distance from the 

 inlet opening, and parallel with and lying along the inner circumference of 

 the measuring vessel. The top cover of the measuring vessel is properly 

 dished out, so as to allow of two small soft iron armatures, fixed to a thin 

 metal arm or needle, to be brought outside the vessel, as near as can be to 

 the poles of the magnets inside ; the metal arm or needle is fixed to a light 

 spindle, carrying an archimedean screw, which further gears with the regis- 

 tering parts of the apparatus. It is evident that the water in passing through 

 the measuring vessel, or rather alongside the same, communicates its motion 

 to the water inside the measuring vessel, which motion is also communicated to 

 the float and magnets, and lastly to the needle and worm spindle and further 



